(CNN) -- A tip to hotel owners: For happy customers, offer wireless internet and a free breakfast, be sure to have smoke-free rooms and keep the level of service consistently high across your properties.

All those factors are key in helping ensure guest contentment, according to the J.D. Power and Associates 2010 North America Hotel Guest Satisfaction Index Study released Tuesday.

It found that guests' overall satisfaction with hotels has improved over last year, especially when it came to the cost of their stay, the reservations process and the quality of their room.

The survey also discovered that 58 percent of hotel guests now book their room online -- a slight increase over last year -- and they're more likely to use the hotel brand's portal than any other site.

"Guests who make reservations directly through the hotel -- whether via phone or website -- are notably more satisfied with their overall experience than guests who book through an independent travel website," said Mark Schwartz, director of the global hospitality and travel practice at J.D. Power and Associates, in a statement.

"Twice as many guests experienced problems with their reservation when booking through independent sites, compared with hotel brand websites."

Overall satisfaction also drops when guests see a difference in service from one hotel to another within the same brand, so delivering a consistent product is critical, Schwartz said.

Expecting Wi-Fi

When it comes to must-have amenities, hotel guests named wireless internet access, complimentary breakfast, bedding and pillow choices, pillow-top mattresses and free parking as their top five choices, according to the study.

More than three-quarters of respondents said they have used Wi-Fi rather than cable internet connections in their room.

"Guests are starting to expect wireless internet access in their hotel rooms," Schwartz said. "Being able to use mobile devices or computers without interruption is considered a comfort of home that should extend to the hotel experience."

But it often comes at a price: Luxury and upscale hotels are less likely to offer complimentary Wi-Fi than mid-scale and extended stay properties.

Meanwhile, any hint of cigarette smoke is a big turnoff to most hotel guests: Eighty-seven percent of respondents said they prefer a smoke-free environment.

Who is tops?

When it came to individual hotel chains, the study included these findings:

• The Ritz-Carlton ranked highest in overall satisfaction in the luxury hotel category, followed by Four Seasons Hotels and Resorts and JW Marriott.

• In the upscale segment, Omni Hotels, Embassy Suites and Renaissance Hotels and Resorts claimed the top three spots.

• Hilton Garden Inn was rated tops in the mid-scale full service category, while Drury Inn & Suites got the thumbs-up in the mid-scale limited service segment.

• Guests staying at economy hotels were most satisfied with Microtel Inns & Suites for the ninth year in a row, followed by Howard Johnson Express/Inns and Red Roof Inn.